Head mounted displays (HMDs) that are mounted on the head of a user have been developed to provide a display to the eye of the user. Such a HMD may use a video see-through approach or an optical see-through approach. In the video see-through approach, the external light is blocked; and only an image is shown. In the optical see-through approach, an image is shown by being superimposed onto the external light image. Viewing is difficult in the optical see-through approach because the image is superimposed onto the external light image.